1. Field of the Invention
The invention relates generally to apparatus for detection of the proper function of an electric fence and/or a fence charger intended to maintain charge on the fence. More particularly, the invention relates to a compact and durable sensing device which can be readily mounted to an electric fence for detecting proper operation of the fence and of a charging device intended to maintain a charge on the fence.
2. Description of the Prior Art
The imposition of an electrical charge on fencing intended to maintain livestock within a specified area has become well known as an alternative or addition to the fencing of livestock or the like by means of conventional fencing intended to retain such stock by virtue of the strength of the fencing rather than by an electrical charge which causes the stock to avoid the fencing. Electric fencing is charged to an appropriate voltage by means of fence charging apparatus which typically apply either continuous or pulsed current to at least one electrical conductor comprising the fencing. Examples of presently available electric fence chargers include the random pulse charging apparatus of Phillips et al which is disclosed in U.S. Pat. No. 4,316,232. McKissack, in U.S. Pat. No. 4,859,869, discloses the use of transformers for applying a continuous charge for energization of an electric fence. Standing, in U.S. Pat. Nos. 4,394,583 and 4,691,084, describe electrical fence chargers as does Shaw et al in U.S. Pat. No. 5,381,298.
While electric fence and fence charger combinations usually provide satisfactory operation, certain circumstances can occur whereby a fence can lose its electrical charge either by failure of the fence charger or by damage to the fence itself such as by cutting of the fence or other circumstance which causes an open circuit or "short" condition. While fence charging apparatus may employ visual or audible signals on the apparatus itself to indicate failure or incipient failure of the fence charger, it is not possible to determine these conditions unless personnel are deployed in the area of the fence chargers per se in order to detect such indications. Accordingly, a need has been felt in the art to provide a simple and inexpensive means by which an observer at essentially any location along an electric fence can be informed of the operational state of the electric fence so that a determination can be made in the event of an indicated failure as to whether a failure of the fence charger exists or whether conductive elements of the electric fence have been breached such as by cutting or other separation thus causing an open or short circuit. The art has previously provided monitoring an alarm system used in association with electric fences and fence chargers. Begg, in U.S. Pat. No. 4,523,187, provides one such alarm while Pope et al, in U.S. Pat. No. 4,220,949, provides a fence monitor as does Hamm in U.S. Pat. No. 5,550,530. McCutchan et al, in U.S. Pat. No. 4,297,633, provides remote devices on electric fence sections whereby the devices transmit signals to a central control location. Although the art has provided monitoring and alarm systems such as are represented by the United States patents cited herein, the art continues to feel the need for a compact and inexpensive device which can be placed on a conductive element of an electric fence and which provides a signal, particularly a visual signal in the form of a flashing light, in the event of the inability of a fence charger to maintain an electric charge on the fence or the lack of a charge on the fence such as can occur due to a separation of the electrical conductor of the fence such as by cutting or any separation causing an open or short circuit. The present invention provides in a compact, inexpensive and exceptionally durable apparatus circuitry for sensing the operational state of an electric fence and thus an electric fence charger intended to maintain an electric charge on the fence and in the several embodiments thereof finds compatibility with known fence chargers whether pulse or continuous and in supply voltage ranges of at least 3 to 15 volts DC while being operable within a wide range of temperatures at least from -40.degree. C. to 85.degree. C.